The structure of organic electroluminescent devices (OLEDs) in which organic semiconductors are used as functional materials is described, for example, in U.S. Pat. Nos. 4,539,507, 5,151,629, EP 0676461 and WO 98/27136. Emitting materials used are frequently organometallic complexes which exhibit phosphorescence rather than fluorescence. For quantum-mechanical reasons, up to four times the energy efficiency and power efficiency is possible using organometallic compounds as phosphorescent emitters. In general terms, there is still a need for improvement in OLEDs, especially also in OLEDs which exhibit triplet emission (phosphorescence), for example with regard to efficiency, operating voltage and lifetime.
The properties of phosphorescent OLEDs are not just determined by the triplet emitters used. More particularly, the other materials used, for example matrix materials, are also of particular significance here. Improvements to these materials can thus also lead to distinct improvements in the OLED properties.
According to the prior art, among other materials, indolocarbazole derivatives (for example according to WO 2007/063754 or WO 2008/056746) or indenocarbazole derivatives (for example according to WO 2010/136109 or WO 2011/000455), especially those substituted by electron-deficient heteroaromatics such as triazine, are used as matrix materials for phosphorescent emitters. In addition, for example, bisdibenzofuran derivatives (for example according to EP 2301926) are used as matrix materials for phosphorescent emitters. However, there is still a need for improvement in the case of use of these matrix materials, especially in relation to the efficiency, the lifetime and the operating voltage of the device.